This section is intended to provide a background or context to the invention disclosed below. The description herein may include concepts that could be pursued, but are not necessarily ones that have been previously conceived, implemented or described. Therefore, unless otherwise explicitly indicated herein, what is described in this section is not prior art to the description in this application and is not admitted to be prior art by inclusion in this section. Abbreviations that may be found in the specification and/or the drawing figures are defined below at the end of the specification but prior to the claims.
LTE UEs for Rel-11 onwards will measure interference from specified interference measurement resources (IMRs). The resources for an assigned IMR most likely will be periodic with a 5 ms period (or a multiple of 5 ms), so that the resources are compatible with legacy Rel-10 UEs. In a heterogeneous network (HetNet) deployment employing eICIC in the form of almost blank subframes (ABSs) or low-power subframes (LPSs), the ABS/LPS pattern is derived with 4 or 8 ms periodicity to be compatible with HARQ timing (especially for UL transmission). As a consequence of this, a UE would be able to sample interference (measured from IMR) for ABS/LPS subframes at periods or 20 ms or 40 ms. This creates a very sparse sampling of interference, thereby degrading link adaptation performance. Secondly, this forces IMR allocation to be linked with ABS pattern design, which adds a level of complexity to network planning.
Workarounds consist of using subframe subsets with a single IMR configuration (corresponding to a single CSI process). A subframe subset is a subset of subframes as configurable by a LTE Rel-10 or above base-station for restricting the measurement of interference by a LTE Rel-10 and above UE. Two subframe subsets can be configured for a given UE by a base-station. This workaround will provide sub-optimal performance with eICIC due to the relatively few opportunities of interference measurement by UEs in protected subframes such as the subframes corresponding to ABS or LPS. Protected sub frames are the subframes that are not ABS/LPS but are subframes that are protected by ABS/LPS subframes at an aggressor eNB. An aggressor eNB is an eNB that can cause significant interference to the UE (the UE that is configured with subframe subsets) when using non-ABS/non-LPS subframes for transmission.
Therefore, it would be beneficial to provide improved opportunities for measuring interference by UEs for systems using interference coordination between cells (such as eICIC).